Community Research and Development Information Service - CORDIS

FP7

ALAMSA Report Summary

Project ID: 314768
Funded under: FP7-TRANSPORT
Country: United Kingdom

Periodic Report Summary 2 - ALAMSA (A Life-cycle Autonomous Modular System for Aircraft Material State Evaluation and Restoring System)

Project Context and Objectives:
The regular maintenance and inspection of aerospace structures offer a big return in reliability and cost savings since in-service damage/ flaws, defects can lead to catastrophic and expensive failures. Currently more than 33% of an average aircraft’s life cycle cost is invested in inspection and repair. Classical NDT/SHM techniques based on linear methods are quite advanced and mature. These techniques have demonstrated excellent results and are frequently used in routine inspections, although there some techno-economical limitations such as inability to detect small defects before they grow to a critical size and difficulties in interpretation. Despite the increased use and the development of nondestructive evaluation methods for material inspection, aircraft materials eventually fail.
This industrial landscape is naturally focusing on the development and implementation of more accurate autonomous systems with modular intelligent functions where automatic/self-monitoring and self-healing concepts are intrinsically linked. The use of novel self-healing material solutions and more reliable automated inspection systems can improve safety, quality and productivity and at the same time provide a decrease in maintenance costs by strongly reducing inspection times and increasing inspection intervals.
ALAMSA will develop a Material State Evaluation and Restoring System for aircraft structures by linking novel automatic self-monitoring systems to a smart in-situ “self-repair” capability that can actively re-establish the continuity and integrity of identified flaws/damage, leading to continuously monitored and restored material integrity. The automated self-monitoring built-in system will have a multi-level role. It will act as a “trigger mechanism” allowing the discrimination of defects and material failure in a timely manner and be smart enough to compute the degree of malfunction and to assess autonomously in an active and remote mode whether aircraft structures need the intervention of a “self-healing recovery program” for rapid repair and redeployment. Hence continued aircraft operation together with the evaluation of the restored properties following the healing process is feasible.
The main objectives of this project are to:

• Develop thermo-reversible self-healing materials which use multiple repair mechanisms, with improved healing efficiencies and system robustness.
• Develop and optimize a new advanced concept for smart inspection and maintenance by employing Nonlinear Elastic Wave Spectroscopy technology in the development of Nonlinear Imaging (NIM) systems for the detection of early stage damage/defects during manufacturing and in-service loading of aerostructures and assessment of the quality of the proposed self-repair technique.
Nonlinear Elastic Wave Spectroscopy (NEWS) methods are an innovative class of vibro-acousto-ultrasound non-destructive techniques that measure nonlinear anomalies in the frequency spectrum in the kHz and MHz range which result from material damage/flaws, with an extreme sensitivity in diagnosing manufacturing defects and damage such as microcracks, delaminations, clapping areas, adhesive bond weakening. NEWS methods are superior to traditional NDT techniques such as classical linear acoustic/ultrasound methods.

Project Results:
At the end of the third year of the project most of the objectives have been achieved and even over exceeded. The design and manufacturing of conventional samples/components with artificial and realistic well defined damage scenarios and samples with self-healing capabilities was continued to further investigate and verify the capabilities of novel Nonlinear Imaging Methods (NIM) for material and structural failure identification.
Both extrinsic and intrinsic healing concepts were further analysed. The study on extrinsic healing by using compartmented fibres focuses on two different aspects: (i) synthesis, manufacturing and characterization of self-healing thermoset materials with compartmented fibres (ii) tuning and reinforcing of the mechanical properties of the alginate fibres. As for intrinsic healing based on ionomers, new nanocomposites were studied. High levels of strain recovery (70-100%) were obtained for both types of polymers after multiple straining cycles. Composite samples containing self-healing Diels-Alder resin were designed and developed. The healing behaviour was assessed by flexural test, optical microscopy and nanoindentation. Also, the ability to recover scratch flaws was verified by optical microscopy.
Three different classes of NIM (NEWS-based surface imaging, NEWS-based tomography and NEWS-based time reversal) for the identification, detection and localization of introduced defects/damage and self-healing capabilities were improved/developed.
Numerical schemes (Finite Elements, Finite Integration Technique, Discontinuous Galerkin Method) and 3-D material models were developed to simulate the interaction of nonlinear elastic wave with the material damage under impact loads and to optimize the proposed NIM and multiple-healing system with a continuous interaction and feedback. A damage propagation model was developed to understand the impact loading damage threshold and the limitations of the self-healing mechanism to selected layers inside the composite laminates. This provides guidelines for the optimal procedure for the activation of self-repair techniques. Concerning the description of material models in solids with complex geometries and localized nonlinearity, the progress relates to the modelling of three-dimensional constitutive material models for defects with a complex geometry which gives rise to the generation of localized sources of nonlinearity. A multiscale material model that is able to simulate the nonlinear interaction of ultrasound waves with cracks/damage precursors in isotropic and anisotropic media was developed. Contact mechanic models were developed and implemented in the COMSOL Multiphysics software. Delaminated composite plates instrumented with a sparse array of transducer elements were modeled to test the potential of RAPID, both in linear and nonlinear operational mode. Also, nonlinear wave propagation models were tested for the nonlinear air-coupled emission (NACE) at delaminations and surface breaking cracks and investigation of local defect resonance (LDR) at delaminations and surface breaking cracks.
Suggestions for optimal pre and post-processing techniques to improve the excitation of high amplitude signals and enhancing the analysis of second order effects in the received signals, induced by the nonlinearity was also developed. As a support to data inversion, numerical approaches were applied to sparse array generated nonlinear wave propagation in order to improve the localization of defects.
The performance of the different classes of NIMs were tested on a selection of samples to show the potential of these techniques for damage detection. In many cases very promising results were obtained, even on complex samples, showing the potential of these methods as damage monitoring techniques. A new patented transducer was developed and tested to enhance thermosonic defect response and image contrast.
A number of techniques were developed based on the concept of LDR on composites. This led to a significant improvement of both efficiency and sensitivity in resonant NIM techniques avoiding high-power instrumentation and makes NIM apparatuses compatible with conventional low-energy ultrasonic equipment. Various experimental NIM techniques were developed based on LDR including nonlinear Resonant Scanning Laser Vibrometry (RESLV), Resonant Thermosonics (RET), and Resonant Shearosonic mode (RESH). Particular attention was paid to develop baseline free approaches to localize and image defects in composites and to optimize the excitation of nonlinear features. Standard nondestructive testing was compared with the results obtained by the nonlinear methodologies developed by the project partners. This was proved on structures made with conventional and novel self-healing materials. Ultrasonic birefringence technique and aircoupled ultrasound were developed and applied successfully to monitor intrinsic and extrinsic self-healing and its efficiency. The testing results proved the viability of this nonlinear methodology to image various defects in composite materials (delaminations, impacts, cracks) for both laboratory-scale samples and realistic aviation related components. This confirms that all the proposed techniques have potential for actual implementation in nondestructive testing or in structural health monitoring. Some applications have already been marketed by the industrial partners. They are widely known to ultrasonic community and recognized to be on the cutting edge of nonlinear ultrasonic research and applications.
During this reporting period, the ALAMSA partners published 19 papers in high-profile peer-reviewed journals (Materials Science and Technology, Journal of Applied Physics, Applied Physics Letters, Journal of NDE, Ultrasonics, Smart Materials Structures, etc.). Eighteen publications were made in International Conference/workshop Proceedings.
The ALAMSA partners were also involved in dissemination of the results working as members of the organizing and scientific committees of multiple international conferences. The project participants made 51 presentations on International Conferences and Exhibitions in Europe and overseas including invited and plenary presentations. A special session on nonlinear NDE/NDT was organized by IKT- University of Stuttgart at International Congress on Ultrasound. Another special session was organized on nonlinear NDE/NDT at International Symposium on non destructive characterization of materials in the US. Academic activities on dissemination of the ALAMSA methodology included weekly seminars on physical and nonlinear acoustics for PhD students and university classes. The practical opportunities of the nonlinear methodology applications in aviation and composite material industries were discussed at the meetings between partners and the industry representatives/users (e.g. Airbus, Agusta Westland, Rolls Royce, BASF, Ceram-Tech industry, Zeppelin aviation company).

Potential Impact:
The major expected scientific and technological impact results at the end of the project are:
1. Development of novel imaging techniques of specific nonlinear type of damage (porosity, microcracking, debonding etc...). It is expected an enhancement of the accuracy to be of an order of magnitude with respect to classical linear techniques.
2. Rapid inspection of structures with complex materials and geometries (double curvatures etc...) with contact and non-contact technologies.
3. Assessment of the efficiency of a new multiple in-situ activated “repair-and-go” material system and verification of its full efficiency and limitations.
Aerospace structures have one of the highest payoffs for maintenance inspection applications since damage can lead to catastrophic and expensive failures and the vehicles involved are required to undergo regular costly inspections. Typically more than 30% of an average aircraft’s life cycle cost is spent on inspection and repair and this figure does include the missing profits associated with the time the aircraft is grounded for scheduled replacements of aircraft components. By substantially reducing maintenance costs and increasing product reliability through the use of automated systems, profit can increase accordingly. Typically, the profit loss of immobilizing a commercial (>150 seats) airplane on the ground for maintenance is in the order of 250000 € per day.
By developing highly sensitive nonlinear imaging techniques for damage diagnostics and visualization, combined with novel self-healing materials, ALAMSA responds to the urgent need for more reliable and less time-consuming quality control systems, maintenance concepts and technologies that enable ‘smart’ aircraft maintenance and contribute to the dreamed long-term vision of ‘maintenance-free’ aircraft. The quality control and inspection technologies developed within ALAMSA will result in a significant improvement in aircraft life, passenger safety, product quality and operating time, at the same time contributing to substantial cost savings. In particular, the result of the project will contribute to the reduction of direct costs of operation due to less ground time and effort spent on inspections and maintenance. By continuously monitoring potential damage, in-situ and at an early stage, it will be possible to induce self-repair or safely schedule inspections without the need to ground the aircraft immediately.
Significant scientific and technological advances will be made by developing a dual automated-monitoring and “repair and go” technology, and the project results will have the power to cause a step change in air transport in the long term.

List of Websites:
go. bath.ac.uk/

Contact

Hazel Wallis, (Head of Research Support and Funding)
Tel.: +44 1225 386822
Fax: +44 1225 386590
E-mail
Record Number: 184002 / Last updated on: 2016-06-09
Information source: SESAM